tests/codegen/casm.c: Move to casm.i (#4662)

Don't call the C preprocessor as it may fail in a cross-compilation
environment. Drop the `-mtriple` argument and let the test run on all
platforms.

Signed-off-by: Andrei Horodniceanu <[email protected]>

Author: the-horo

tests/codegen/casm.c

@@ -0,0 +1,4 @@
+// RUN: %ldc -output-ll -of=%t.ll %s && FileCheck %s < %t.ll
+
+// CHECK: module asm ".symver __qsort_r_compat, qsort_r@FBSD_1.0"
+asm(".symver " "__qsort_r_compat" ", " "qsort_r" "@" "FBSD_1.0");